1. Field of the Invention
The present invention relates to a sheet conveying apparatus that pinches a sheet to be conveyed, and an image forming apparatus that forms an image on the conveyed sheet.
2. Description of the Related Art
An image forming apparatus such as a printer, a copier, and a facsimile machine pinches a sheet such as roll paper, a role film, and a cut-sheet with a conveyance roller and a pinch roller that is driven by the conveyance roller. The sheet is conveyed by the rotating conveyance roller, whereby an image is formed on the sheet in the image forming section.
A mechanism is conventionally known which a user can manually release a sheet pinched by a conveyance roller and a pinch roller. The mechanism allows a user to operate an operation lever to separate the pinch roller from the conveyance roller to release the pinching state. In a case where a roll sheet is loaded after the release, a leading edge of the sheet is sent into a sheet discharging section via a conveyance section and an image forming section, and then the operation lever is returned to the original position to press the pinch roller towards the conveyance roller side to pinch the sheet. In a case where roll paper left in the conveyance section due to paper-jamming is to be removed, the operation lever is manually operated to release the pinch roller in the pinching state and then the sheet is returned to the upper stream side before rewinding.
In order to improve the above complex manual operation by the user, an apparatus is provided which executes a release of a pinched sheet by a drive motor. More specifically, a mechanism is provided which moves a pinch roller by a force of an electric driving source according to an instruction from the user or a detection signal of paper-jamming. Return of the sheet to the pinching state after the release processing is also performed by a drive motor (Refer to Japanese Patent Application Laid-Open No. 11-91986, and Japanese Patent Application Laid-Open No. 2006-315816.)
In an apparatus which moves a pinch roller by a drive motor, the pinch roller may suspend its operation at an unexpected position relative to the conveyance roller while the sheet is left in the image forming section when the apparatus encounters an unexpected technical issue such as a power drop caused by power failure during use, or suspension of an operation caused by a system error. In a recovery operation, complex procedures need to be taken. Namely, the user powers on the apparatus again and gives the apparatus an instruction to release pinching of the sheet. Then, the user resets the remaining sheets at the correct positions before giving the apparatus an instruction to execute the pinching operation again.
Removing and resetting of the remaining sheets can be carried out faster if the user manually opens and closes the pinch roller of the apparatus in a powered off state. An apparatus discussed in the above patent documents is, however, equipped with no mechanism for manually opening and closing the pinch roller, therefore, the possibility of a fast recovery operation is reduced in the above complex procedures.
Supposing the apparatus is powered on while the sheet remains in the image forming section, a head loaded on a carriage can contact the sheet and be damaged due to movement of the carriage in the image forming section in the scanning direction. If the apparatus is powered on to execute a recovery in a state where the pinch roller does not completely contact the conveyance roller, the pinch roller may hit the carriage and cause damage to the carriage.